linux-kernel - Re: [PATCH] printf: fix Woverride-init warning for EDEADLK errno

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Date:   Tue, 27 Oct 2020 07:55:47 +0100
From:   Uwe Kleine-König <uwe@...ine-koenig.org>
To:     Arnd Bergmann <arnd@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Petr Mladek <pmladek@...e.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] printf: fix Woverride-init warning for EDEADLK errno

Good morning Arnd,

On 10/26/20 10:49 PM, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> On most architectures, gcc -Wextra warns about the list of error
> numbers containing both EDEADLK and EDEADLOCK:
> 
> lib/errname.c:15:67: warning: initialized field overwritten [-Woverride-init]
>    15 | #define E(err) [err + BUILD_BUG_ON_ZERO(err <= 0 || err > 300)] = "-" #err
>       |                                                                   ^~~
> lib/errname.c:172:2: note: in expansion of macro 'E'
>   172 |  E(EDEADLK), /* EDEADLOCK */
>       |  ^
> lib/errname.c:15:67: note: (near initialization for 'names_0[35]')
>    15 | #define E(err) [err + BUILD_BUG_ON_ZERO(err <= 0 || err > 300)] = "-" #err
>       |                                                                   ^~~
> lib/errname.c:172:2: note: in expansion of macro 'E'
>   172 |  E(EDEADLK), /* EDEADLOCK */
>       |  ^

bad performance of gcc to warn twice about the same line and not
mentioning the line that has E(EDEADLOCK).

> Make that line conditional on the two values being distinct.
> 
> Fixes: 57f5677e535b ("printf: add support for printing symbolic error names")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  lib/errname.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/lib/errname.c b/lib/errname.c
> index 0c4d3e66170e..6adff0bf2445 100644
> --- a/lib/errname.c
> +++ b/lib/errname.c
> @@ -169,7 +169,9 @@ static const char *names_0[] = {
>  	E(ECANCELED), /* ECANCELLED */
>  	E(EAGAIN), /* EWOULDBLOCK */
>  	E(ECONNREFUSED), /* EREFUSED */
> +#if EDEADLK != EDEADLOCK
>  	E(EDEADLK), /* EDEADLOCK */
> +#endif

The comments suggest that duplicates are expected. Would it make sense
to add similar conditions to the other three entries?

Best regards
Uwe

>  };
>  #undef E
>  




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